In dairy farming operations, milk from the dairy herd conventionally is stored in a refrigerated milk bulk tank. Periodically, the milk in the bulk tank is transferred to a milk tank truck for delivery to a dairy, cheese factory, or the like. Such trucks typically collect milk from several farms, all of which milk is combined within the single tank of the truck.
The price received by the farmer for his milk is determined in part by the butterfat content of the milk. Because the milk is mixed in the tank truck with that of other farmers, it is necessary to obtain samples of the milk for measurement of butterfat before it is transferred from the bulk tank to the truck. Butterfat tends to float to the top of the unhomogenized milk in the bulk tank. Consequently, it is necessary to stir or otherwise agitate the milk before the sample is taken so that the butterfat is uniformly redistributed through the milk and the sample taken is typical of the whole. Conventionally, the milk tank truck driver activates an agitator within the bulk tank for a standardized length of time, usually from 5 to 10 minutes, before taking the sample and then pumping the bulk tank out.
Problems arise when inattentive or hurried tank truck drivers agitate the milk in the bulk tank for an insufficiently long period of time before sampling it. The sample is conventionally taken from the midst of the tank. Consequently, when the milk has not been thoroughly agitated, the sample is at best inaccurate. Typically it contains less butterfat than it would if the agitation had been carried on for the prescribed length of time, leading to a low price for the milk.
The technical field is generally cognizant of the need to control the agitation of milk in a farm bulk milk tank and the like for various reasons. Fleck, U.S. Pat. No. 3,731,494 provides for the timed agitation of milk in a bulk tank for various purposes. Fleck further provides for the automatic agitation of milk when the temperature of the milk is above a selected level. A manual control is provided for timed agitation of the milk prior to the taking of butterfat samples, the manual control being adapted to override the automatic, temperature responsive control. Girton, et al., U.S. Pat. Nos. 2,875,590 and 2,875,591 disclose a system for interconnecting the agitating and cooling functions of a milk bulk tank, providing for an interlock between cooling and agitating functions and a weighing function of the device shown.
The technical field is not cognizant of means for preventing the removal of milk from a milk bulk tank before agitation of the milk sufficient to ensure that a reliable butterfat sample may be taken.